Reflective image-forming optical system, exposure apparatus, and device manufacturing method

ABSTRACT

A reflective imaging optical system which forms, on a second plane, an image of a pattern arranged on a first plane and illuminated with light from an illumination optical system includes a plurality of reflecting mirrors including first and second reflecting mirrors by which the light reflected by the first plane is reflected first, second, respectively. An area on the first plane illuminated with the light from the illumination optical system is an illumination objective area, the illumination objective area is positioned on a predetermined side of an optical axis of the reflecting mirrors, and reflection areas of the first and second reflecting mirrors are positioned on the predetermined side of the optical axis of the reflecting mirrors; and the first and second reflecting mirrors are arranged so that an optical path of the light from the illumination optical system is positioned between the first and second reflecting mirrors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional of U.S. patent application Ser. No. 14/451,699filed Aug. 5, 2014, which in turn is a Continuation of InternationalApplication No. PCT/JP2013/051961 filed Jan. 30, 2013, which claims theconventional priority of Japanese Patent Application No. 2012-023167filed on Feb. 6, 2012 and titled “Reflective Imaging Optical System,Exposure Apparatus, and Method for Producing Device”. The disclosures ofeach of the prior applications is incorporated herein by reference inits entirety.

BACKGROUND

Field of the Invention

The present invention relates to a reflective (catoptric) imagingoptical system, an exposure apparatus, and a method for producing adevice. More specifically, the present invention relates to a reflectiveimaging optical system suitable for an exposure apparatus which uses,for example, the EUV light (EUV light beam) and transfers, onto aphotosensitive substrate, a circuit pattern on a mask in accordance withthe mirror projection method.

Description of the Related Art

Attention is directed to an EUVL (Extreme UltraViolet Lithography)exposure apparatus which uses the EUV (Extreme UltraViolet) light havinga wavelength of, for example, about 5 nm to 40 nm as an exposureapparatus to be used for producing semiconductor elements, etc. In acase that the EUV light is used as the exposure light (exposure lightbeam), any usable transmissive optical material and any useable dioptricoptical material are absent. Therefore, a reflection type mask is used,and a reflective optical system (optical system constructed of onlyreflecting members) is used as a projection optical system.

Conventionally, it has been suggested that a reflective optical system,which has an entrance pupil disposed on a side opposite to the opticalsystem with an object plane intervening therebetween (an entrance pupildisposed on a side opposite to the optical system with respect to anobject plane), is used as a reflective imaging optical system applicableto a projection optical system of an EUV exposure apparatus, in place ofa reflective optical system which has an entrance pupil disposed on aside of the optical system with respect to an object plane (see, forexample, U.S. Pat. No. 6,781,671). In the following description of thisspecification, the “reflective imaging optical system having theentrance pupil disposed on the side of the optical system with respectto the object plane” is referred to as “reflective imaging opticalsystem of the near pupil type”, and the “reflective imaging opticalsystem having the entrance pupil disposed on the side opposite to theoptical system with respect to the object plane” is referred to as“reflective imaging optical system of the far pupil type”. The former isalso referred to as “reflective imaging optical system of the normalpupil type” and the latter is also referred to as “reflective imagingoptical system of the opposite pupil type”.

SUMMARY

In a case that a conventional reflective imaging optical system of thefar pupil type is applied to the EUV exposure apparatus, an angle formedby the optical path of light coming into an oblique incidence mirror(flat mirror) of an illumination optical system and the optical axis ofthe reflective imaging optical system is relatively large. As a result,the size or dimension of footprint (installation area) of the EUVexposure apparatus in the scanning direction is relatively large, whichincreases the cost of manufacture, installation, and the like of theapparatus.

The aspects of the present teaching have been made taking the foregoingproblems into consideration, an object of which is to provide areflective imaging optical system which can reduce the footprint of anexposure apparatus to which the reflective imaging optical system isapplied. The exposure apparatus may be an exposure apparatus using, forexample, the EUV light. Further, another object of the present teachingis to perform the projection exposure at a high resolution whilesecuring a large resolving power by applying the reflective imagingoptical system of the present teaching to a projection optical system ofan exposure apparatus and using, for example, the EUV light as anexposure light.

In order to solve the problems as described above, according to a firstembodiment of the present teaching, there is provided a reflectiveimaging optical system which forms, on a second plane, an image of apattern arranged on a first plane and illuminated with light from anillumination optical system, the reflective imaging optical systemcomprising:

a plurality of reflecting mirrors including a first reflecting mirror bywhich the light reflected by the first plane is reflected first, and asecond reflecting mirror by which the light reflected by the first planeis reflected second,

wherein an area on the first plane illuminated with the light from theillumination optical system is an illumination objective area, theillumination objective area is positioned on a predetermined side withrespect to an optical axis of the plurality of reflecting mirrors, and areflection area of the first reflecting mirror and a reflection area ofthe second reflecting mirror are positioned on the predetermined sidewith respect to the optical axis of the plurality of reflecting mirrors;and

the first reflecting mirror and the second reflecting mirror arearranged so that an optical path of the light from the illuminationoptical system is positioned between the first reflecting mirror and thesecond reflecting mirror.

According to a second embodiment of the present teaching, there isprovided a reflective imaging optical system which forms, on a secondplane, an image of a pattern arranged on a first plane and illuminatedwith light from an illumination optical system, the reflective imagingoptical system comprising:

a plurality of reflecting mirrors including a first reflecting mirror bywhich the light reflected by the first plane is reflected first, asecond reflecting mirror by which the light reflected by the first planeis reflected second, and a third reflecting mirror by which the lightreflected by the first plane is reflected third,

wherein the first reflecting mirror and the second reflecting mirror arearranged so that an optical path of the light from the illuminationoptical system is positioned between a reflection area of the firstreflecting mirror and a reflection area of the second reflecting mirror;and

an area on the first plane illuminated with the light from theillumination optical system is an illumination objective area, theillumination objective area is positioned on a predetermined side withrespect to an optical axis of the plurality of reflecting mirrors, andthe third reflecting mirror is arranged on the predetermined side withrespect to the optical axis of the plurality of reflecting mirrors.

According to a third embodiment of the present teaching, there isprovided an exposure apparatus, comprising:

an illumination optical system which illuminates a pattern arranged on afirst plane with light from a light source; and

the reflective imaging optical system as defined in the first embodimentor the second embodiment which projects the pattern on the first planeon a photosensitive substrate disposed on the second plane.

According to a fourth embodiment of the present teaching, there isprovided a method for producing a device, comprising:

exposing a photosensitive substrate with a pattern by using the exposureapparatus as defined in the third embodiment;

developing the photosensitive substrate to which the pattern has beentransferred to form a mask layer, which has a shape corresponding to thepattern, on a surface of the photosensitive substrate; and

processing the surface of the photosensitive substrate via the masklayer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a construction of an exposure apparatusaccording to an embodiment of the present teaching.

FIG. 2 shows a positional relationship between an optical axis and acircular arc-shaped effective imaging area formed on a wafer.

FIG. 3 schematically shows a construction of a reflective imagingoptical system according to a first embodiment of the present teaching.

FIG. 4 schematically shows a construction of a reflective imagingoptical system according to a second embodiment of the present teaching.

FIGS. 5A to 5C illustrate that uneven illuminance in an illuminationarea is suppressed to be small in the embodiment.

FIG. 6 is a drawing to explain a conditional expression in theembodiment.

FIG. 7 is a flow chart concerning an exemplary technique adopted when asemiconductor device is obtained as a microdevice.

DESCRIPTION OF THE EMBODIMENTS

In the following, an embodiment of the present teaching will beexplained based on the accompanying drawings. FIG. 1 schematically showsa construction of an exposure apparatus according to the embodiment ofthe present teaching. FIG. 2 shows a positional relationship between anoptical axis and a circular arc-shaped effective imaging area formed ona wafer. In FIG. 1, the Z axis is defined in the direction of theoptical axis AX of a reflective imaging optical system 6, i.e., in thenormal direction of an exposure surface (transfer surface) of a wafer 7provided as a photosensitive substrate, the Y axis is defined in thedirection parallel to the sheet surface of FIG. 1 in the exposuresurface of the wafer 7, and the X axis is defined in the directionperpendicular to the sheet surface of FIG. 1 in the exposure surface ofthe wafer 7. A first direction and a predetermined direction correspondto, for example, a direction parallel to the Y axis (Y axis direction).

With reference to FIG. 1, a light source 1 which is provided to supplythe exposure light includes, for example, a laser plasma X-ray source.Those usable as the light source 1 include discharge plasma lightsources and other X-ray sources. The light (light beam) radiated fromthe light source 1 comes into an illumination optical system IL, via anoptionally arranged wavelength selective filter (not shown). Thewavelength selective filter has such a characteristic that only the EUVlight having a predetermined wavelength (for example, 13.4 nm), which isincluded in the lights supplied by the light source 1, is selectivelytransmitted through the wavelength selective filter, and thetransmission of the lights having other wavelengths is shielded or shutoff by the wavelength selective filter.

The EUV light allowed to pass through the wavelength selective filter isguided to an optical integrator 2 constructed of a pair of fly's eyeoptical systems (fly's eye mirrors) 2 a, 2 b. Note that instead ofproviding the wavelength selective filter, it is allowable to form amulti-layered film, which reflects only a EUV light having apredetermined wavelength, on a reflecting surface of a mirror whichreflects or collects generated EUV light. In this case, there is no needto provide any wavelength selective filter, and thus it is possible toachieve a compact-sized light source 1. Further, it is possible toprevent the light amount loss in the EUV light in the wavelengthselective filter.

The first fly's eye optical system 2 a has a plurality of firstreflecting optical elements which are arranged in juxtaposition or inparallel. The second fly's eye optical system 2 b has a plurality ofsecond reflecting optical elements which are arranged in juxtapositionor in parallel to correspond to the plurality of first reflectingoptical elements of the first fly's eye optical system 2 a.Specifically, the first fly's eye optical system 2 a is constructed, forexample, by arranging a large number of concave mirror elements, havingcircular arc-shaped outer shapes, densely, laterally and longitudinally.The second fly's eye optical system 2 b is constructed, for example, byarranging a large number of concave mirror elements, which haverectangular outer shapes, densely, laterally and longitudinally.Reference may be made, for example, to United States Patent ApplicationPublication No. 2002/0093636 A1 about detailed construction and functionof the fly's eye optical systems 2 a, 2 b. The contents of United StatesPatent Application Publication No. 2002/0093636 A1 are incorporatedherein by reference in their entirety.

Thus, a substantial surface light source, which has a predeterminedshape, is formed in the vicinity of the reflecting surface of the secondfly's eye optical system 2 b. The substantial surface light source isformed at the position of the exit pupil (exit pupil position) of theillumination optical system IL constructed of the pair of fly's eyeoptical systems 2 a, 2 b. The exit pupil position of the illuminationoptical system IL (i.e., the position in the vicinity of the reflectingsurface of the second fly's eye optical system 2 b) is coincident withthe position of the entrance pupil of the reflective imaging opticalsystem (projection optical system) 6 of the far pupil type.

The light from the substantial surface light source, i.e., the lightexiting or irradiated from the optical integrator 2 comes into a flatmirror 3 which functions as an oblique incidence mirror. The lightreflected by the flat mirror 3 passes between a first reflecting mirrorM1 and a second reflecting mirror M2 of the reflective imaging opticalsystem 6, and then forms a circular arc-shaped illumination area(illumination objective area) on the mask 4 via a circular arc-shapedaperture (light-transmitting portion) of a field stop (not shown) whichis arranged closely to the reflection type mask 4 substantially inparallel thereto.

In this way, the optical integrator 2 (2 a, 2 b) and the flat mirror 3constitute the illumination optical system IL which is provided toperform the Koehler illumination for the mask 4 provided with apredetermined pattern by use of the light from the light source 1. Noreflecting mirror having any power is arranged in the optical pathbetween the second fly's eye optical system 2 b and the mask 4. Thepower of the reflecting mirror is a reciprocal of the focal length orfocal distance of the concerning reflecting mirror. It is allowable thatthe reflecting mirror having any power may be arranged in the opticalpath between the second fly's eye optical system 2 b and the mask 4.

The mask 4 is held by a mask stage 5 which is movable in the Y directionso that the pattern surface of the mask 4 extends along the XY plane.The movement of the mask stage 5 is measured by a laser interferometerand an encoder which are omitted from the illustration. For example, acircular arc-shaped illumination area, which is symmetrical in relationto the Y axis, is formed on the mask 4. The light, which comes from theilluminated mask 4, forms a pattern image of the mask 4 on a wafer 7 asa photosensitive substrate, via the reflective imaging optical system 6.

That is, as shown in FIG. 2, a circular arc-shaped effective imagingarea (static exposure area) ER, which is symmetrical in relation to theY axis, is formed on the wafer 7. With reference to FIG. 2, the circulararc-shaped effective imaging area ER, which has a length LX in the Xdirection and a length LY in the Y direction, is formed in the circulararea (image circle) IF which has the optical axis AX as the center andhas a radius Y0, in a manner that the effective imaging area ER is incontact with the image circle IF. The circular arc-shaped effectiveimaging area ER is a part of the annular or zonal area provided aboutthe center of the optical axis AX. The length LY is the widthwisedimension of the effective imaging area ER provided in the directionconnecting the optical axis and the center of the circular arc-shapedeffective imaging area ER.

The wafer 7 is held by a wafer stage 8 which is two-dimensionallymovable in the X direction and the Y direction so that the exposuresurface of the wafer 7 extends along the XY plane. The movement of thewafer stage 8 is measured by a laser interferometer and an encoder whichare omitted from the illustration, in the same manner as the mask stage5. Thus, the scanning exposure (scanning and exposure) is performedwhile the mask stage 5 and the wafer stage 8 are moved in the Ydirection, i.e., the mask 4 and the wafer 7 are relatively moved in theY direction with respect to the reflective imaging optical system 6. Bydoing so, the pattern of the mask 4 is transferred to an exposure areaof the wafer 7.

In a case that the projection magnification (transfer magnification) ofthe reflective imaging optical system 6 is ⅛, the synchronous scanningis performed by setting the movement velocity of the wafer stage 8 to ⅛of the movement velocity of the mask stage 5. The pattern of the mask 4is successively transferred to respective exposure areas of the wafer 7by repeating the scanning exposure while the wafer stage 8 istwo-dimensionally moved in the X direction and the Y direction. Theprojection magnification of the reflective imaging optical system 6 maybe ⅙, ¼, or the like. For example, in a case that the projectionmagnification of the reflective imaging optical system 6 is ⅙, themovement velocity of the wafer stage 8 is set to ⅙ of the movementvelocity of the mask stage 5. In a case that the projectionmagnification of the reflective imaging optical system 6 is ¼, themovement velocity of the wafer stage 8 is set to ¼ of the movementvelocity of the mask stage 5.

In the embodiment of the present teaching, as shown in FIGS. 3 and 4,the reflective imaging optical system 6 concerning each of embodimentsincludes, along the single optical axis AX extending in a form ofstraight line, a first reflective optical system G1 which forms anintermediate image of the pattern at a position optically conjugate withthe pattern surface of the mask 4 (hereinafter referred also to as “masksurface”), and a second reflective optical system G2 which forms, on atransfer surface of the wafer 7 (hereinafter referred also to as “wafersurface”), a final reduced image (image of the intermediate image) ofthe pattern of the mask 4. That is, the position, which is opticallyconjugate with the illumination area on the pattern surface of the mask4, is formed in the optical path between the first reflective opticalsystem G1 and the second reflective optical system G2. The reflectiveimaging optical system 6 may be constructed only of the first reflectiveoptical system G1 or may be constructed by use of a plurality of opticalsystems such as a third reflective optical system and a fourthreflective optical system.

The first reflective optical system G1 includes the first reflectingmirror M1 which has a concave (concave surface-shaped) reflectingsurface, the second reflecting mirror M2 which has a convex (convexsurface-shaped) reflecting surface, a third reflecting mirror M3 whichhas a concave (concave surface-shaped) reflecting surface or a convex(convex surface-shaped) reflecting surface, a fourth reflecting mirrorM4 which has a concave (concave surface-shaped) reflecting surface, afifth reflecting mirror M5 which has a convex (convex surface-shaped)reflecting surface, and a sixth reflecting mirror M6 which has a concave(concave surface-shaped) reflecting surface, as referred to in an orderof the incidence of the light (in an order in which they reflect thelight travels from the mask 4 toward the wafer 7).

The second reflective optical system G2 includes a seventh reflectingmirror M7 which has a convex (convex surface-shaped) reflecting surfaceand a eighth reflecting mirror M8 which has a concave (concavesurface-shaped) reflecting surface as referred to in an order of theincidence of the light. The reflecting surfaces of respective reflectingmirrors M1 to M8 may be constructed of the reflecting surfaces in aconcave-surface shape, a convex-surface shape, plane-surface shape, andother curved shapes, respectively.

In the respective embodiments, an aperture stop AS (not shown) isprovided at a position at which the reflecting surface of the fourthreflecting mirror M4 is located or at a position in the vicinitythereof. The aperture stop AS sets the numerical aperture of thereflective imaging optical system 6 by limiting the light flux of theexposure light. For example, the aperture stop AS may be a variableaperture stop capable of adjusting the dimension or size of the aperture(aperture size), or a switching member provided with a plurality ofapertures having mutually different size, shape, etc., and capable ofchoosing a desired aperture from the plurality of apertures.

In the respective embodiments, the light from an illumination area whichis separated from the optical axis AX in the −Y direction on the patternsurface of the mask 4 (first plane) is successively reflected by thereflecting surface of the first reflecting mirror M1, the reflectingsurface of the second reflecting mirror M2, the reflecting surface ofthe third reflecting mirror M3, the reflecting surface of the fourthreflecting mirror M4, the reflecting surface of the fifth reflectingmirror M5, and the reflecting surface of the sixth reflecting mirror M6,and then the reflected light forms the intermediate image of the maskpattern. The light from the intermediate image formed via the firstreflective optical system G1 is successively reflected by the reflectingsurface of the seventh reflecting mirror M7 and the reflecting surfaceof the eighth reflecting mirror M8, and then the reflected light formsan reduced image of the mask pattern at an effective imaging area ERwhich is separated from the optical axis AX in the −Y direction on thesurface of the wafer 7 (second plane).

Specifically, the magnitude of the imaging magnification of thereflective imaging optical system 6 according to a first embodiment is⅛, and the magnitude of the imaging magnification of the reflectiveimaging optical system 6 according to a second embodiment is ⅙.Therefore, the reduced image of ⅛ times the mask pattern is formed atthe effective imaging area ER in the first embodiment, and the reducedimage of ⅙ times the mask pattern is formed at the effective imagingarea ER in the second embodiment.

In the respective embodiments, the eight mirrors which are the first toeighth reflecting mirrors M1 to M8 constructing the reflective imagingoptical system 6 are arranged so that the centers of curvature(curvature centers) of the reflecting surfaces of the first to eighthreflecting mirrors M1 to M8 are positioned on the optical axis AX havinga form of straight line. The reflecting mirrors M1 to M8 have theaspheric reflecting surfaces each of which is formed along the surfacerotationally symmetric about the optical axis AX. In a case that thereflecting surface is formed to be an aspherical surface, it is possibleto use the paraxial center of curvature as the center of curvature ofthe reflecting surface. In the vicinity of the intersection pointbetween the axis of rotational symmetry and the aspherical surface, theaspherical surface may be considered as a spherical surface, and thecenter of curvature of this spherical surface is referred to as theparaxial center of curvature (apex center of curvature). The reflectiveimaging optical system 6 may be constructed of, for example, 7 to 12reflecting mirrors.

In the respective embodiments, the reflective imaging optical system 6is the optical system which is substantially telecentric on the side ofthe wafer (on the side of the image). In other words, in the respectiveembodiments, the main light beam, which arrives at the respectivepositions on the image plane of the reflective imaging optical system 6,is substantially perpendicular to the image plane. Owing to thisconstruction, the imaging can be performed satisfactorily even whenirregularities (protrusions and recesses) within the depth of focus ofthe reflective imaging optical system 6 exists on the wafer. Thereflective imaging optical system 6 concerning each of the embodimentsis the reflective imaging optical system of the far pupil type which hasthe entrance pupil, at the position separated from the reflectiveimaging optical system by a predetermined distance, the position beingon the side opposite to the reflective imaging optical system 6 withrespect to the mask 4.

In this embodiment, the light reflected by the flat mirror 3 of theillumination optical system IL passes between the first reflectingmirror M1 and the second reflecting mirror M2, and then forms a circulararc-shaped illumination area which is separated from the optical axis AXin the −Y direction on the mask 4. That is, the first reflecting mirrorM1 and the second reflecting mirror M2 are arranged so that the opticalpath of the light coming from the illumination optical system IL ispositioned therebetween. Further, the reflection area of the firstreflecting mirror M1 and the reflection area of the second reflectingmirror M2 are positioned in the −Y direction of the optical axis AX.Here, the “reflection area” can mean the radiation area of light whichis formed on the reflecting surface of a reflecting mirror by the lightcoming into the reflecting mirror. In a case that the radiation area ofthe light which is formed on the reflecting surface of a reflectingmirror by the light coming into the reflecting mirror is changeddepending on the illumination conditions and the like, a maximumradiation area can be regarded as the “reflection area”. In a case thatthere are a plurality of radiation areas of the light which are formedon the reflecting surface of a reflecting mirror by the light cominginto the reflecting mirror, the area, which includes all of theplurality of radiation areas on the reflecting surface and has a minimumarea or dimension, may be regarded as the “reflection area”. Inparticular, in the respective embodiments, the first reflecting mirrorM1 to the third reflecting mirror M3 are positioned in the −Y directionof the optical axis AX, and the reflection area of the first reflectingmirror M1 is formed to be farther away from the optical axis AX than thereflection area of the second reflecting mirror M2.

Accordingly, in this embodiment, the angle formed by the optical path oflight coming into the flat mirror 3 of the illumination optical systemIL and the optical axis AX of the reflective imaging optical system 6can be suppressed to be small. Thus, the size of the footprint(installation area) of the EUV exposure apparatus in the scanningdirection can be suppressed to be small, thereby making it possible toreduce the cost of manufacture, installation, and the like of theapparatus. In order to make the angle formed by the optical path of thelight coming into the flat mirror 3 and the optical axis AX small and inorder to make the footprint of the apparatus small, it is preferred thatan acute angle formed by the plane formed by extending the reflectingsurface of the flat mirror 3 and the flat surface on which the patternsurface of the mask 4 is positioned be set to 60 degrees or more.

The structure of this embodiment in which the first reflecting mirror M1and the second reflecting mirror M2 are arranged so that the opticalpath of the light coming from the illumination optical system IL ispositioned therebetween is easily obtained by setting the magnitude ofthe imaging magnification of the reflective imaging optical system 6 toa value smaller than ¼ which is normally used, for example ⅛ or ⅙. Thereason thereof is as follows. That is, in a case that the magnitude ofthe imaging magnification is made to be smaller while the numericalaperture on the image side of the reflective imaging optical system 6 issecured to be required magnitude, the cross-sections of light fluxcoming into the first reflecting mirror M1 and the second reflectingmirror M2 become smaller and thus it is possible to secure a large spacebetween the first reflecting mirror M1 and the second reflecting mirrorM2.

The structure in this embodiment can make the incident angle of thelight beam to the flat mirror 3 larger than those of conventional art,and thus the reflectance in the flat mirror 3 which is larger than thoseof conventional art can be secured. Accordingly, the light amount lossin the flat mirror 3 can be suppressed to be small. Further, since theincident angle of the light beam to the flat mirror 3 is larger thanthose of conventional art, the uneven illuminance in the Y direction inthe illumination area on the mask 4 can be suppressed to be small asshown in FIGS. 5A to 5C.

FIG. 5A illustrates the incident angle characteristic of reflectance ofthe flat mirror. With reference to FIG. 5A, in a case that the flatmirror is used for the light beam in a range 51 of which incident angleis relatively small like conventional art, a relatively great changeoccurs in the reflectance depending on the incident angle. Thus, asshown in FIG. 5B, there is caused a relatively large uneven illuminancein the Y direction in the illumination area. On the other hand, in acase that the flat mirror 3 is used for the light beam in a range 52 ofwhich incident angle is relatively large like this embodiment, thereflectance substantially stays constant with little dependence on theincident angle. Thus, as shown in FIG. 5C, the uneven illuminance in theY direction in the illumination area can be suppressed to be small. Thereflecting surface of the flat mirror is formed of a single layer filmor multi-layer film. By adjusting the number of layers, the thickness ofthe film, the material of the film, and the like, it is possible to useflat mirrors having various incident angle characteristics.

In this embodiment, as shown in FIG. 6, in a case that a distance, inthe Y direction, between a reflection area M1 a of the first reflectingmirror M1 and a reflection area M2 a of the second reflecting mirror M2is referred to as “H”, and that the cross-section dimension of thereflection area M1 a of the first reflecting mirror M1 in the Ydirection is referred to as “D”, the following conditional expression(1) may be satisfied.

0.5<D/H<1.1  (1)

In a case that D/H becomes less than the lower limit of the conditionalexpression (1), the light coming into the mask 4 passes between thefirst reflecting mirror M1 and second reflecting mirror M2 at a positionwhere the cross-section dimension D is relatively small, that is, aposition which is relatively close to the mask 4. Thus, there is fearthat the second reflecting mirror M2 is too close to the mask 4 toarrange. Or, the distance H becomes relatively large to make theincident angle of the light beam coming into the mask 4 and the incidentangle of the light beam coming into the first reflecting mirror M1large. Thus, the reflectance in the mask 4 and the reflectance in thefirst reflecting mirror M1 are reduced, which could cause the decreasein throughput of the apparatus owing to the light amount loss in themask 4 and the first reflecting mirror M1. Further, since the incidentangle of the light beam coming into the mask 4 and the incident angle ofthe light beam coming into the first reflecting mirror M1 become large,there is fear that the image of the pattern of the mask 4 is not formedon the exposure surface of the wafer 7 with high accuracy due to theprotrusions and recesses of the pattern of the mask 4. Examples of thecase in which the image of the pattern of the mask 4 is not formed onthe exposure surface of the wafer 7 with high accuracy due to theprotrusions and recesses of the pattern of the mask 4 include thedecrease in imaging performance due to the shadow caused by theprotrusions and recesses of the pattern, the light amount loss caused bythe interception or blocking of the light coming into the mask 4 owingto the protrusions and recesses of the pattern, and the like.

In a case that D/H exceeds the upper limit of the conditional expression(1), there is fear that the light coming into the mask 4 interferes withthe first reflecting mirror M1 and the second reflecting mirror M2.Therefore, in a case that the conditional expression (1) is satisfied,the space between the mask 4 and the second reflecting mirror M2 can besecured. This brings an advantage such that the first reflecting mirrorM1 and the second reflecting mirror M2 can be arranged easily. In thecase that the conditional expression (1) is satisfied, it is possible tomake the incident angle of the light beam coming into the mask 4 and theincident angle of the light beam coming into the first reflecting mirrorM1 small. Thus, the decrease in reflectance in the mask 4 and the firstreflecting mirror M1 can be suppressed, which improves the throughput ofthe exposure apparatus. Further, the deterioration in imaging due to theprotrusions and recesses of the pattern of the mask 4 is suppressed,which makes it possible to form the image of the pattern of the mask 4on the exposure surface of the wafer 7 with high accuracy. Furthermore,it is possible to suppress the influence caused when the light cominginto the mask 4 interferes with the first reflecting mirror M1 and thesecond reflecting mirror M2. In order to obtain better effect of thisembodiment, the lower limit of the conditional expression (1) may be setto 0.75 or 0.9. The cross-section dimension D may be the dimension of anarea, in the Y direction, which is obtained by projecting the reflectionarea M1 a of the first reflecting mirror M1 on a plane perpendicular tothe optical axis. Or, the cross-section dimension D may be the dimensionof an area, in the Y direction, which is positioned on the plane(depicted by the broken line extending horizontally in FIG. 6) includingthe position of the first reflecting mirror M1 and being perpendicularto the optical axis, and which is occupied by the light coming into thepattern surface of the mask 4. In this case, the position of the firstreflecting mirror M1 may be a position, in the circumferential portionof the reflection area M1 a of the first reflecting mirror M1, closestto the optical axis, or the position of the first reflecting mirror M1may be a position, in the circumferential portion of the reflection areaM1 a of the first reflecting mirror M1, farthest away from the opticalaxis.

In the respective embodiments of the present teaching, an asphericalsurface is expressed by the following numerical expression (a) providedthat y represents the height in the direction perpendicular to theoptical axis, z represents the distance (sag amount) along the opticalaxis from the tangent plane, at the apex of the aspherical surface, tothe position on the aspherical surface at the height y, r represents theapex radius of curvature, κ represents the conical coefficient, andC_(n) represents the n-order aspherical coefficient.

$\begin{matrix}{z = {{\left( {y^{2}\text{/}r} \right)\text{/}\left\{ {1 + \left\{ {1 - {\left( {1 + \kappa} \right)*y^{2}\text{/}r^{2}}} \right\}^{1\text{/}2}} \right\}} + {C_{4} \cdot y^{4}} + {C_{6} \cdot y^{6}} + {C_{8} \cdot y^{8}} + {C_{10} \cdot y^{10}} + {C_{12} \cdot y^{12}} + {C_{14} \cdot y^{14}} + {C_{16} \cdot y^{16}}}} & (a)\end{matrix}$

First Embodiment

FIG. 3 shows a construction of a reflective imaging optical systemaccording to a first embodiment of the present teaching. With referenceto FIG. 3, in the reflective imaging optical system 6 of the firstembodiment, the light from the mask 4 is successively reflected by theconcave reflecting surface of the first reflecting mirror M1, the convexreflecting surface of the second reflecting mirror M2, the concavereflecting surface of the third reflecting mirror M3, the concavereflecting surface of the fourth reflecting mirror M4, the convexreflecting surface of the fifth reflecting mirror M5, and the concavereflecting surface of the sixth reflecting mirror M6 and then thereflected light forms the intermediate image of the mask pattern.

The light from the intermediate image formed via the first reflectiveoptical system G1 is successively reflected by the convex reflectingsurface of the seventh reflecting mirror M7 and the concave reflectingsurface of the eighth reflecting mirror M8, and then the reflected lightforms the reduced image (secondary image) of the mask pattern on thewafer 7. In the first embodiment, the magnitude R of imagingmagnification of the reflective imaging optical system 6 is ⅛, and theacute angle formed by the plane formed by extending the reflectingsurface of the flat mirror 3 and the mask surface is 82 degrees. In thefirst embodiment, an aperture stop AS (not shown in the drawing) isarranged at a position of the reflecting surface of the fourthreflecting mirror M4 or at a position in the vicinity thereof. Theaperture stop AS may be provided at a location between the thirdreflecting mirror M3 and the fourth reflecting mirror M4, a locationbetween the fourth reflecting mirror M4 and the fifth reflecting mirrorM5, a position conjugate to the reflecting surface of the fourthreflecting mirror M4 or a position in the vicinity thereof, or the like.

Table 1 described below shows values of items or elements of thereflective imaging optical system according to the first embodiment. Inthe column of the major items shown in Table 1, λ represents thewavelength of the exposure light, β represents the magnitude of theimaging magnification, NA represents the numerical aperture on the imageside (wafer side), Y0 represents the radius (maximum image height) ofthe image circle IF on the wafer 7, LX represents the size or dimensionin the X direction of the effective imaging area ER, and LY representsthe size or dimension in the Y direction of the effective imaging areaER (widthwise dimension of the circular arc-shaped effective imagingarea ER).

In the column of the optical member items shown in Table 1, the surfacenumber represents the sequence or order of the reflecting surface ascounted from the mask side in the direction in which the light travelsfrom the mask surface as the object plane (pattern surface of the mask4) to the wafer surface as the image plane (transfer surface of thewafer 7), r represents the apex radius of curvature (central radius ofcurvature: mm) of each of the reflecting surfaces, and d represents thespacing distance on the axis of each of the reflecting surfaces, i.e.,the inter-surface spacing (mm). The sign of the inter-surface spacing dis changed every time when the reflection occurs. The radius ofcurvature of the surface convex towards the mask is set to be positive,and the radius of curvature of the surface concave from the mask is setto be negative, irrelevant to the direction of the incidence of thelight.

In the column of the values corresponding to the conditional expressionshown in Table 1, H represents the distance in the Y direction providedbetween the reflection area of the first reflecting mirror M1 and thereflection area of the second reflecting mirror M2 and D represents thecross-section dimension of the reflection area of the first reflectingmirror M1 in the Y direction. Further, as reference values, PDrepresents the distance (entrance pupil distance) along the optical axisbetween the entrance pupil and the mask surface, TT represents thedistance (total length) along the optical axis between the mask surfaceand the wafer surface, and R represents the angle of incidence (rad) ofthe main light beam coming into the mask surface. The incident angle Rshall take a negative value in a case that a main light beam reflectedby the mask surface travels in a direction away from the optical axisAX. The foregoing notation also holds in Table 2 described later on inthe same manner as described above.

TABLE 1 Major Items: λ = 13.4 nm β = ⅛ NA = 0.5 Y0 = 41.50 mm LX = 13 mmLY = 1.0 mm Optical Member Items: Surface No. r d Optical member (mask500.907 surface) 1 −845.540 −222.994 (first reflecting mirror M1) 2−603.806 744.907 (second reflecting mirror M2) 3 −2020.053 −521.813(third reflecting mirror M3) 4 2387.067 402.377 (fourth reflectingmirror M4) 5 626.102 −769.948 (fifth reflecting mirror M5) 6 1091.8321232.057 (sixth reflecting mirror M6) 7 321.642 −249.299 (seventhreflecting mirror M7) 8 312.976 279.299 (eighth reflecting mirror M8)(wafer surface) Aspherical Data: First Surface: κ = 0 C₄ = −1.144837 ×10⁻¹⁰ C₆ = 5.754085 × 10⁻¹⁵ C₈ = −3.181161 × 10⁻²⁰ C₁₀ = 8.709635 ×10⁻²⁶ C₁₂ = 1.427421 × 10⁻³¹ C₁₄ = −1.571308 × 10⁻³⁶ C₁₆ = 2.986494 ×10⁻⁴² Second Surface: κ = 0 C₄ = 3.088833 × 10⁻⁹ C₆ = −3.862657 × 10⁻¹⁵C₈ = −6.508134 × 10⁻²⁰ C₁₀ = 1.362713 × 10⁻²⁴ C₁₂ = −1.364423 × 10⁻²⁹C₁₄ = 7.539638 × 10⁻³⁵ C₁₆ = −1.736016 × 10⁻⁴⁰ Third Surface: κ = 0 C₄ =4.963271 × 10⁻¹⁰ C₆ = −5.030842 × 10⁻¹⁶ C₈ = −5.182840 × 10⁻²¹ C₁₀ =1.059625 × 10⁻²⁵ C₁₂ = −1.865317 × 10⁻³⁰ C₁₄ = 2.229099 × 10⁻³⁵ C₁₆ =−1.077214 × 10⁻⁴⁰ Fourth Surface: κ = 0 C₄ = −1.827048 × 10⁻⁹ C₆ =−3.415226 × 10⁻¹⁴ C₈ = −7.848731 × 10⁻¹⁹ C₁₀ = −4.096783 × 10⁻²³ C₁₂ =2.385006 × 10⁻²⁷ C₁₄ = −2.702122 × 10⁻³¹ C₁₆ = 8.240540 × 10⁻³⁶ FifthSurface: κ = 0 C₄ = −1.6573.97 × 10⁻¹⁰ C₆ = −3.847514 × 10⁻¹⁵ C₈ =1.539176 × 10⁻²¹ C₁₀ = −1.124299 × 10⁻²⁵ C₁₂ = −1.652992 × 10⁻²⁹ C₁₄ =7.264395 × 10⁻³⁴ C₁₆ = −8.630798 × 10⁻³⁹ Sixth Surface: κ = 0 C₄ =5.036087 × 10⁻¹³ C₆ = 7.415084 × 10⁻¹⁸ C₈ = −3.171087 × 10⁻²³ C₁₀ =1.080338 × 10⁻²⁸ C₁₂ = −2.093168 × 10⁻³⁴ C₁₄ = 2.262700 × 10⁻⁴⁰ C₁₆ =−1.018244 × 10⁻⁴⁶ Seventh Surface: κ = 0 C₄ = 1.730920 × 10⁻⁸ C₆ =9.395766 × 10⁻¹³ C₈ = 2.795811 × 10⁻¹⁷ C₁₀ = 9.026776 × 10⁻²² C₁₂ =−7.149350 × 10⁻²⁵ C₁₄ = 1.275899 × 10⁻²⁸ C₁₆ = −1.905227 × 10⁻³² EighthSurface: κ = 0 C₄ = 4.947677 × 10⁻¹⁰ C₆ = 6.365871 × 10⁻¹⁵ C₈ = 7.433736× 10⁻²⁰ C₁₀ = 6.347248 × 10⁻²⁵ C₁₂ = 1.849725 × 10⁻²⁹ C₁₄ = −1.997201 ×10⁻³⁴ C₁₆ = 5.448389 × 10⁻³⁹ Values Corresponding to the ConditionalExpression: D = 59.120 mm H = 80.829 mm PD = 3269.1 mm TT = 1395.5 mm R= −0.100 (1) (D/H) = 0.73

In relation to the reflective imaging optical system of the firstembodiment, the value of RMS (root mean square) of the wavefrontaberration was determined for the respective points in the circulararc-shaped effective imaging area ER. As a result, the maximum value(worst value) was 0.0335λ (λ: wavelength of light=13.4 nm). That is, inthe first embodiment, it is possible to secure the relatively largenumerical aperture on the image side of 0.5, and it is possible tosecure the circular arc-shaped effective imaging area of 13 mm×1.0 mm inwhich the various aberrations are satisfactorily corrected on the wafer.Further, in the first embodiment, a spacing distance of not less than 8mm is secured between each of the reflecting mirrors and the light fluxpassing in the vicinity of each of the reflecting mirrors.

Second Embodiment

FIG. 4 shows a construction of a reflective imaging optical systemaccording to a second embodiment of the present teaching. With referenceto FIG. 4, in the reflective imaging optical system 6 according to thesecond embodiment, the light from the mask 4 is successively reflectedby the concave reflecting surface of the first reflecting mirror M1, theconvex reflecting surface of the second reflecting mirror M2, the convexreflecting surface of the third reflecting mirror M3, the concavereflecting surface of the fourth reflecting mirror M4, the convexreflecting surface of the fifth reflecting mirror M5, and the concavereflecting surface of the sixth reflecting mirror M6 and then thereflected light forms the intermediate image of the mask pattern.

The light from the intermediate image formed via the first reflectiveoptical system G1 is successively reflected by the convex reflectingsurface of the seventh reflecting mirror M7 and the concave reflectingsurface of the eighth reflecting mirror M8, and then the reflected lightforms the reduced image of the mask pattern on the wafer 7. In thesecond embodiment, the magnitude P of imaging magnification of thereflective imaging optical system 6 is ⅙, and the acute angle formed bythe plane formed by extending the reflecting surface of the flat mirror3 and the mask surface is 83 degrees. In the second embodiment also, anaperture stop AS (not shown in the drawing) is arranged at a position ofthe reflecting surface of the fourth reflecting mirror M4 or at aposition in the vicinity thereof, in a similar manner as in the firstembodiment. Table 2 described below shows values of items or elements ofthe reflective imaging optical system according to the secondembodiment.

TABLE 2 Major Items: λ = 13.4 nm β = ⅙ NA = 0.5 Y0 = 38.50 mm LX = 17.4mm LY = 1.0 mm Optical Member Items: Surface No. r d Optical member(mask 366.0731 surface) 1 −581.254 −173.077 (first reflecting mirror M1)2 −504.217 186.217 (second reflecting mirror M2) 3 2858.152 −279.214(third reflecting mirror M3) 4 1048.798 548.844 (fourth reflectingmirror M4) 5 527.506 −622.001 (fifth reflecting mirror M5) 6 1024.6351376.692 (sixth reflecting mirror M6) 7 297.840 −201.0245 (seventhreflecting mirror M7) 8 257.429 231.024 (eighth reflecting mirror M8)(wafer surface) Aspherical Data: First Surface: κ = 0 C₄ = 6.334772 ×10⁻¹⁰ C₆ = 4.053272 × 10⁻¹⁵ C₈ = −7.133735 × 10⁻²⁰ C₁₀ = 4.505447 ×10⁻²⁵ C₁₂ = 5.903391 × 10⁻³⁰ C₁₄ = −9.187387 × 10⁻³⁵ C₁₆ = 3.506429 ×10⁻⁴⁰ Second Surface: κ = 0 C₄ = 1.052386 × 10⁻⁸ C₆ = −1.895379 × 10⁻¹³C₈ = 7.258412 × 10⁻¹⁸ C₁₀ = −2.430244 × 10⁻²² C₁₂ = 5.402014 × 10⁻²⁷ C₁₄= −6.950205 × 10⁻³² C₁₆ = 3.953995 × 10⁻³⁷ Third Surface: κ = 0 C₄ =8.030029 × 10⁻⁹ C₆ = −4.277496 × 10⁻¹⁴ C₈ = 1.207719 × 10⁻¹⁸ C₁₀ =−1.625005 × 10⁻²² C₁₂ = 1.515615 × 10⁻²⁶ C₁₄ = −7.180262 × 10⁻³¹ C₁₆ =1.457437 × 10⁻³⁵ Fourth Surface: κ = 0 C₄ = −1.883268 × 10⁻⁹ C₆ =−5.233724 × 10⁻¹⁴ C₈ = −1.628503 × 10⁻¹⁸ C₁₀ = −8.808161 × 10⁻²³ C₁₂ =3.386588 × 10⁻²⁷ C₁₄ = −6.590832 × 10⁻³¹ C₁₆ = 1.746258 × 10⁻³⁵ FifthSurface: κ = 0 C₄ = −1.345956 × 10⁻⁹ C₆ = −3.897405 × 10⁻¹⁷ C₈ =4.264561 × 10⁻²¹ C₁₀ = −4.238677 × 10⁻²⁵ C₁₂ = 6.574421 × 10⁻³⁰ C₁₄ =−6.369767 × 10⁻³⁵ C₁₆ = 3.112936 × 10⁻⁴⁰ Sixth Surface: κ = 0 C₄ =−4.780883 × 10⁻¹² C₆ = −1.808289 × 10⁻¹⁸ C₈ = −1.356320 × 10⁻²³ C₁₀ =3.000797 × 10⁻²⁹ C₁₂ = −6.505272 × 10⁻³⁵ C₁₄ = 6.859371 × 10 ⁻⁴¹ C₁₆ =−3.918473 × 10⁻¹⁷ Seventh Surface: κ = 0 C₄ = 2.767278 × 10⁻⁸ C₆ =2.037818 × 10⁻¹² C₈ = 4.818580 × 10⁻⁴⁷ C₁₀ = 1.116519 × 10⁻²⁰ C₁₂ =−8.332805 × 10⁻²⁴ C₁₄ = 2.030806 × 10⁻²⁷ C₁₆ = −2.880151 × 10⁻³¹ EighthSurface: κ = 0 C₄ = 7.979056 × 10⁻¹⁰ C₆ = 1.600529 × 10⁻¹⁴ C₈ = 2.902626× 10⁻¹⁹ C₁₀ = 2.810315 × 10⁻²⁴ C₁₂ = 2.205571 × 10⁻²⁸ C₁₄ = −4.796949 ×10⁻³³ C₁₆ = 1.422134 × 10⁻³⁷ Values Corresponding to the ConditionalExpression: D = 56.463 mm H = 54.874 mm PD = 2163.4 mm TT = 1433.5 mm R= −0.105 (1) (D/H) = 1.03

In relation to the reflective imaging optical system of the secondembodiment, the maximum value (worst value) of RMS of the wavefrontaberration was 0.0266λ (λ: wavelength of light=13.4 nm). That is, alsoin the second embodiment, it is possible to secure the relatively largenumerical aperture on the image side of 0.5 in the same manner as in thefirst embodiment, and it is possible to secure the circular arc-shapedeffective imaging area of 17.4 mm×1.0 mm in which the variousaberrations are satisfactorily corrected on the wafer. Further, in thesecond embodiment, a spacing distance of not less than 8 mm is securedbetween each of the reflecting mirrors and the light flux passing in thevicinity of each of the reflecting mirrors similar to the firstembodiment.

In the respective embodiments described above, it is possible to securethe satisfactory imaging performance and the relatively large numericalaperture on the image side of 0.5, and it is possible to secure thecircular arc-shaped effective imaging area of 13 mm×1.0 mm or 17.4mm×1.0 mm in which the various aberrations are satisfactorily correctedon the wafer 7, with respect to the EUV light having the wavelength of13.4 nm. Therefore, the pattern of the mask 4 can be transferred at thehigh resolution of not more than 0.1 m by the scanning exposure to eachof the exposure areas having the size of, for example, 13 mm×16.5 mm or17.4 mm×22.0 mm on the wafer 7.

In the respective embodiments described above, the EUV light having thewavelength of 13.4 nm is used by way of example. However, there is nolimitation to this. The present teaching is also applicable similarly orequivalently to a reflective imaging optical system which uses, forexample, the EUV light having a wavelength of about 5 nm to 40 nm or anyother light having an appropriate wavelength.

In the respective embodiments described above, the reflective imagingoptical system 6 includes the eight reflecting mirrors M1 to M8 whereinthe centers of curvature of the reflecting surfaces are arranged on thesame axis (on the optical axis AX). However, at least one of the eightreflecting mirrors M1 to M8 may be provided such that the center ofcurvature of the reflecting surface is deviated or shifted from theoptical axis AX. In the respective embodiments described above, all ofthe reflecting mirrors M1 to M8 have the reflecting surfaces formedalong a surface which is infinite-fold rotational symmetry in relationto the optical axis AX. However, at least one of the reflecting mirrorsM1 to M8 may have a reflecting surface formed along a surface which isn-fold rotational symmetry in relation to the optical axis AX (“n” isfinite number, for example, one, two or three).

In the respective embodiments described above, the present teaching isapplied to the reflective imaging optical system of the far pupil type.However, there is no limitation to this. The present teaching is alsoapplicable similarly or equivalently to any reflective imaging opticalsystem of the near pupil type. In the reflective imaging optical systemof the near pupil type, the entrance pupil is positioned on a side ofthe optical system from the object plane.

In the reflective imaging optical system 6 according to each of theembodiments, the reflecting area of the first reflecting mirror M1 andthe reflecting area of the second reflecting mirror M2 are positioned onthe same side as the illumination objective area (illumination area) onthe pattern surface of the mask M with respect to the optical axis AX ofthe reflective imaging optical system 6. The first reflecting mirror M1and the second reflecting mirror M2 are arranged so that the opticalpath of the light coming from the illumination optical system IL ispositioned therebetween. As a result, the angle formed by the opticalpath of the light coming into the flat mirror 3 of the illuminationoptical system IL and the optical axis AX of the reflective imagingoptical system 6 can be suppressed to be small (82 to 83 degrees), andthus the footprint of the exposure apparatus can be suppressed to besmall.

In the exposure apparatus of this embodiment, the EUV light is used asthe exposure light. Thus, the pattern of the mask M can be projectedonto the wafer W to expose the wafer W therewith at a high resolution byrelatively moving the wafer W and the pattern of the mask M to betransferred relative to the reflective imaging optical system 6. As aresult, a highly accurate device can be produced under the satisfactoryexposure condition by using the scanning type exposure apparatus havinga large resolving power.

The exposure apparatus of the embodiment described above is produced byassembling the various subsystems including the respective constitutiveelements as defined in claims so that the predetermined mechanicalaccuracy, electric accuracy and optical accuracy are maintained. Inorder to secure the various accuracies, those performed before and afterthe assembling include the adjustment for achieving the optical accuracyfor the various optical systems, the adjustment for achieving themechanical accuracy for the various mechanical systems, and theadjustment for achieving the electric accuracy for the various electricsystems. The steps of assembling the various subsystems into theexposure apparatus include, for example, the mechanical connection, thewiring connection of the electric circuits, and the piping connection ofthe air pressure circuits among the various subsystems. It goes withoutsaying that the steps of assembling the respective individual subsystemsare performed before performing the steps of assembling the varioussubsystems into the exposure apparatus. When the steps of assembling thevarious subsystems into the exposure apparatus are completed, theoverall adjustment is performed to secure the various accuracies as theentire exposure apparatus. The exposure apparatus may be produced in aclean room in which the temperature, the cleanness, etc. are managed.

Next, an explanation will be made about a device production method usingthe exposure apparatus according to the embodiment described above. FIG.7 shows a flow chart illustrating steps of producing a semiconductordevice. As shown in FIG. 7, in the steps of producing the semiconductordevice, a metal film is vapor-deposited on a wafer W which is to serveas a substrate of the semiconductor device (Step S40); and thevapor-deposited metal film is coated with a photoresist as aphotosensitive material (Step S42). Subsequently, a pattern formed on amask (reticle) M is transferred to each of shot areas on the wafer W byusing the exposure apparatus of the embodiment described above (StepS44: exposure step). The wafer W for which the transfer has beencompleted is developed, i.e., the photoresist, to which the pattern hasbeen transferred, is developed (Step S46: development step). After that,the resist pattern, which is formed on the surface of the wafer W inaccordance with Step S46, is used as a mask to perform the processingincluding, for example, the etching with respect to the surface of thewafer W (Step S48: processing step).

The resist pattern herein refers to the photoresist layer formed withprotrusions and recesses having shapes corresponding to the patterntransferred by the exposure apparatus of the embodiment described above,wherein the recesses penetrate through the photoresist layer. In StepS48, the surface of the wafer W is processed via the resist pattern. Theprocessing, which is performed in Step S48, includes, for example, atleast one of the etching of the surface of the wafer W and the filmformation of a metal film or the like. In Step S44, the exposureapparatus of the embodiment described above transfers the pattern byusing, as the photosensitive substrate, the wafer W coated with thephotoresist.

In the embodiment described above, the laser plasma X-ray light sourceis used as the light source for supplying the EUV light. However, thereis no limitation to this. It is also possible to use, for example, thesynchrotron radiation (SOR) light as the EUV light.

In the embodiment described above, the present teaching is applied tothe exposure apparatus having the light source for supplying the EUVlight. However, there is no limitation to this. The present teaching isalso applicable to an exposure apparatus having a light source forsupplying a light having any wavelength other than the EUV light.

In the embodiment described above, it is possible to use a variablepattern-forming apparatus for dynamically forming a predeterminedpattern based on predetermined electronic data, instead of using themask M. It is possible to use, as such a variable pattern-formingapparatus, for example, a spatial light modulator including a pluralityof reflecting elements which are driven based on predeterminedelectronic data. The exposure apparatus, which uses the spatial lightmodulator as the variable pattern-forming apparatus, is disclosed, forexample, in United States Patent Application Publication Nos.2007/0296936 and 2009/0122381. The disclosures of United States PatentApplication Publication Nos. 2007/0296936 and 2009/0122381 areincorporated herein by reference in their entirety.

In the embodiment described above, the present teaching is applied tothe reflective imaging optical system provided as the projection opticalsystem of the exposure apparatus. However, there is no limitation tothis. In general, the present teaching is also applicable similarly orequivalently to any reflective imaging optical system in which an imageon the first plane at a predetermined area is formed on the secondplane.

What is claimed is:
 1. A reflective imaging optical system which forms,on a second plane, an image of a pattern arranged on a first plane andilluminated with light from an illumination optical system, thereflective imaging optical system comprising: a plurality of reflectingmirrors including a first reflecting mirror by which the light reflectedby the first plane is reflected first, and a second reflecting mirror bywhich the light reflected by the first plane is reflected second,wherein an area on the first plane illuminated with the light from theillumination optical system is an illumination objective area, theillumination objective area is positioned on a predetermined side withrespect to an optical axis of the plurality of reflecting mirrors, and areflection area of the first reflecting mirror and a reflection area ofthe second reflecting mirror are positioned on the predetermined sidewith respect to the optical axis of the plurality of reflecting mirrors;and the first reflecting mirror and the second reflecting mirror arearranged so that an optical path of the light from the illuminationoptical system is positioned between the first reflecting mirror and thesecond reflecting mirror.